Generally, a driving assistance device including a car navigation system or the like, which is incorporated in a vehicle, calculates a moving time taken from the current location to a destination and the shortest route based on traffic information acquired from a road traffic information communication system. The road traffic information communication system employed in such driving assistance delivers traffic congestion information collected by a road traffic information center, which is the management center of the system, and a variety of traffic information, such as a moving time taken in each section and traffic regulations, to the driving assistance device via a communication medium such as a radio beacon, optical beacon, or FM multiplex broadcasting. The driving assistance device selects a recommended route from the current location to the destination based on, for example, traffic information thus delivered, and informs the driver of the selected recommended route. Additionally, the driving assistance device calculates a moving time on the recommended route taken from the current location to the destination based on, for example, traffic information thus delivered, and informs the driver of the calculated moving time.
When calculating the recommended route and the moving time, such a driving assistance device generally uses a specific road section separated by, for example, nodes such as traffic signals and intersections, that is, a link cost, which is an index indicating the degree of ease of passage set for each link. An example of the link cost is information about average moving time and road width, and the like. The driving assistance device refers to a link cost set for each of links present from the current location to the destination, and selects a route from the current location to the destination to minimize this link cost.
As in the device disclosed in, for example, Patent Document 1, as such a link cost, the cost of power source such as fuel is used, which is stored in storage means in association with a node or link registered in map data in advance. This device manages the cost of a power source, using a node or link as a management unit. When calculating a recommended route and moving time, this device extracts, from the storage means, the link cost of each of travel routes from a starting point to a destination, and performs various operations for calculating the recommended route and moving time based on the extracted link cost.